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IIS and ASP.NET: The Application Pool

  • August 6, 2003
  • By Thiru Thangarathinam
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Configuring Identity for an Application Pool

To demonstrate how to configure the identity for an application pool and how ASP.NET uses that identity information at the execution time, we will create a very simple ASP.NET application. We will start off by creating a new ASP.NET application named IdentityExample by using the New Project dialog box in Visual Studio.NET. After the project is created, if you open up IIS manager, you will find that the IdentityExample project is created in the default application pool named DefaultAppPool.

Now, let us add the following lines of code to the Page_Load event of the default Web form WebForm1.aspx.

private void Page_Load(object sender, System.EventArgs e)
{
  Response.Write(
   "ASP.NET application executes using the
           identity :: <b>" +
    WindowsIdentity.GetCurrent().Name + 
         "</b><br>");
}

As you can see from the above code, we simply display the name of the account that the ASP.NET Web application uses to process the service. If you execute thise code by navigating to the page from the browser, you will see the following output.



Click here for a larger image.

The above output just reinforces the fact that, by default, the Web application runs using the NetworkService account. Let us change the identity of the DefaultAppPool and then look at the output of our Web application. To do this, right-click the DefaultAppPool node from the IIS manager and select Properties from the context menu. In the properties dialog box, navigate to the Identity tab and select the Configurable option and specify a valid user name and password. Once entered, the screen should look like the following.

Now if you execute your application, you will see the following output.



Click here for a larger image.

As expected, the output reflects the change that we made using the IIS manager.

Associating an ASP.NET Web Application with an Application Pool

Create a new Visual Studio.NET project named IISIntegration using the New Project dialog box as shown in the following screen shot.

After creating the new project, if you open up IIS Manager, you will find that the IISIntegration project is created under an application pool named DefaultAppPool. As the name suggests, by default, all the newly created ASP.NET Web applications are created under this application pool. This is shown in the following screen shot.



Click here for a larger image.

To associate the IISIntegration ASP.NET Web application with the application pool named DemoAppPool, select the Web Sites node that is present under the Machine Name node in the IIS manager. Then, select Default Web Site-&IISIntegration from the treeview and right-click it to select Properties from the context menu.

In the Properties dialog box shown above, you can change the Application Pool using the Application Pool dropdown option in the Directory tab. Because we want our Web application to run under the DemoAppPool, select DemoAppPool from the list.

Recycling Worker Processes and Their Impact on Application State Information

If a Web application contains code that causes problems, and you cannot easily rewrite the code, it might be useful to limit the extent of the problems by periodically recycling the worker process that services the application. You can accomplish this by using what is known as Worker Process Recycling. Worker process recycling is the replacing of the instance of the application in memory. IIS 6.0 can automatically recycle worker processes by restarting the worker process, or worker processes, that are assigned to an application pool. This helps keep problematic applications running smoothly, and minimizes problems such as memory leaks. You can trigger the recycling of the worker processes assigned to an application pool by using worker process recycling methods that are based on elapsed time, the number of Hypertext Transfer Protocol (HTTP) requests, a set time of day, and two kinds of memory consumption, in addition to recycling on demand.

To configure all the above settings, go to the Properties window of the application pool in which your Web application is running using the IIS manager. Using the Recycling, Performance, and Health tabs in the Properties window, you can specify values for the above settings. Navigating to the Performance tab in the Properties dialog box of the DemoAppPool results in the following output.

When you set the recycling of worker processes using IIS manager, you also need to take the state management strategy of your ASP.NET application into consideration. Because every time the worker process is recycled, the ASP.NET state information will be lost rendering the application in an invalid state. One alternative to overcome this issue is to maintain state data external to the worker process, such as in a database. However, moving data to an external database to allow recycling can affect server performance in the following two ways:

  • Performance is reduced because of the added data management that is needed to move the data between the application and the database.
  • Recycling flushes any in-process data caches, so the caches need to be rebuilt.

If you have an application pool with applications that depend on state data, you must decide whether or not to recycle the worker processes that are assigned to that application pool. If you store state in the same process as that of IIS, and you don't want the state information to be lost, you must not recycle a worker process using the application pool configuration settings.

Conclusion

In this part, we looked at what application pools are and their role in increasing the reliability of your ASP.NET Web applications. We also understood that by allowing different ASP.NET applications to run under their own application pool, we can also set different identities, thereby controlling the security permissions for different ASP.NET Web applications. In Part-3 of this article, we will discuss the new XML-based Metabase storage and the security features of IIS 6.0.

About the Author

Thiru has six years of experience in architecting, designing, developing and implementing applications using Object Oriented Application development methodologies. He also possesses a thorough understanding of software life cycle (design, development and testing). He is an expert with ASP.NET, .NET Framework, Visual C#.NET, Visual Basic.NET, ADO.NET, XML Web Services and .NET Remoting and holds MCAD for .NET, MCSD and MCP certifications.

Thiru has authored numerous books and articles. He can be reached at thiruthangarathinam@yahoo.com.

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